The question of just what kind of sub was "USS Tiger Fish", from the movie "Ice Station Zebra", depends - literally - on how you want to look at it:

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At left, USS Ronquil - a diesel-electric, Guppy-III Fleet Boat - portrayed TigerFish in the above-surface/closeup scenes of the movie. However in the underwater scenes, as at right, TigerFish was portrayed by a model depicting - quite accurately - a Skate-class nuclear-powered attack sub. Already it can be seen that the sail of the latter is finer, with sides far closer to vertical than on Ronquil's more pyramid-like (Atlantic High) sail. But the two boats differ by far most below the waterline (see below).

Note, above (right), the Skate-class rudders and stern planes basically form a cross, located roughly on the hull centerline-axis. This contrasts sharply with the rudder/stern-planes arrangement of the Guppy-III (or any Fleet Boat):

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Note from this (excellent Chris Porter/IronBottom Sound) model of Ronquil, extending downward from the stern, the rudder and aft diving planes form a sort of inverted "T" - with no top rudder at all. Running a close second to this difference is at the bow - again, mainly below the waterline - where, on the Guppy-III a large boulder-like sonar dome juts down from an otherwise conventionally-tapering and raked/rounded chin. Contrast this with the abrupt right-angle chin of the Skate-class model above, free of any protrusions.

But even above the waterline, differences in the appearance of these two classes are quite noticeable to the discerning eye:

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At top, seen on the surface, Skate herself (12/6/57) exhibits the very straight/vertical look of her sail, as well as the stub of her top rudder (far-right), never seen on any Guppy-III. Note also her deck was extremely narrow - no wider than the sail itself, around whose base a thin lip was required as a foothold - with hull-casing sides accordingly having a pronounced outward slope, as opposed to the relatively wide decks and vertical casing-sides of Ronquil, and all such Fleet Boats based on the Gato/Balao/Tench design. At bottom, the contrast between the Ronquil model (left) and again Skate herself, seen from almost mirror-angles, port and starboard, really makes apparent these differences.

The choice of such a different-looking, Skate-class model for filming the underwater scenes in Ice Station Zebra was no accident, as: 1) TigerFish was, in the screenplay, supposed to be a nuclear sub; and 2) the movie's main plot point - nuclear sub operability under the north polar ice cap - was exactly what the Skate-class SSNs had, in real-life, recently been demonstrating (following the landmark exploit of their direct progenitor, USS Nautilus). Obviously then, it was the use of Ronquil - seeing as how I guess the USN, unbelievable as it may seem, wouldn't make a front-line nuclear attack boat available for filming(!) - which was the film-makers getting as close as they could, with a real-life, submarine stand-in.

So, who should be considered "USS TigerFish", in Ice Station Zebra? There is really no conflict here: USS Ronquil was the actor, while a USS Skate-class boat was the character.